1. Field of the Invention
The present invention is related to an apparatus for automatically releasing the pressure in a pressurized liquid cooling system of an engine when the engine is turned off. More particularly, the present invention is directed to an apparatus comprising a radiator cap having an automatic mechanism for opening the suction return valve in the radiator cap to release cooling system pressure when the engine is turned off and leaving it open until the engine is restarted, utilizing either a vacuum motor or electrical solenoid and pin.
2. Description of Related Art
Engine cooling system components, such as hoses, wear out sooner than they should because they are subjected to superatmospheric pressure when such pressure is not required for engine cooling, that is, after the engine has been turned off. Engine cooling systems operate at superatmospheric pressure to increase the cooling capacity of the coolant and to increase engine efficiency. The engine water jacket, radiator, heater core and the like are typically connected together by a plurality of rubber hoses. Engine passageways are sealed from one another by gaskets. A head gasket, for example, seals the cylinders from the water jacket. These components deteriorate and fail from exposure to heat and pressure. While a certain amount of cooling system pressure may be desirable for proper engine cooling when the engine is running, that pressure is relieved only over the course of 1-5 hours after the engine is turned off, that is, as the engine cools enough to allow the cooling system pressure to fall to atmospheric pressure. The service life of the hoses and similar components would be significantly increased if there was no pressure on them when the engine was not running. Indeed, for many short trips, significant superatmospheric pressure will be exerted on the cooling system for several times as long as the trip actually takes. It is expected that the present invention will extend the life of radiator and heater hoses by at least 25%-30% and will similarly reduce the incidence of costly radiator leaks, depending on vehicle use characteristics.
A second problem is perhaps more serious, as it is safety related. Every year many motor vehicle operators and mechanics are scalded when they open a pressurized radiator. The resulting injuries may be quite serious and require extended and expensive medical care, including plastic surgery. Many devices have been designed that supposedly allow a hot radiator to be opened safely. These devices, however, seem primarily to be in the nature of shields that are intended to prevent the hot cooling fluid from reaching the operator. Moreover, hardly anyone owns such a device. Most people who need access to the cooling system when the engine is hot simply wait, but frequently do not wait long enough for the cooling of the engine to relieve the cooling system pressure. Many accidental injuries could be prevented by a device that automatically releases all superatmospheric pressure on a vehicle cooling system when the engine is not running.
The prior art related references demonstrate that significant effort has been directed to radiator caps for so called closed cooling systems, that is, a cooling system in which coolant that escapes, either through thermal expansion or evaporation, is collected in a coolant recovery tank, where it cools and where vapors condense into liquid, and which is returned to the radiator and cooling system when the engine cools. The references discussed herein, however, do not disclose or suggest any radiator cap or other device that automatically releases the superatmospheric pressure on the cooling system whenever the engine is turned off, which appears to be the only sure and certain way of solving the two problems discussed above. Some of these related art references are discussed below.
A typical prior art radiator cap of the provides access to and protection for the cooling systems of liquid cooled engines, especially the cooling system of vehicle engines, which typically include a water jacket surrounding the cylinders of the engine, a radiator for dissipating excess heat from the engine, and a plurality of rubber hoses for circulating the coolant from the engine into the radiator and back into the engine water jacket. The cooling system also includes other equipment, typically a thermostat for controlling the temperature of the coolant, a heater core and connecting hoses, a heater switch for regulating the flow of coolant through the heater core, and so forth. The prior art radiator cap is designed to permit a predetermined amount of pressure, for example, 15 pounds per square inch (psi), to develop within the cooling system to increase the boiling point, and hence the heat carrying capacity of the coolant. Too much pressure, however, can rupture a hose or other elements of the cooling system, so the radiator cap includes an over pressure release valve designed to open automatically when pressure in the cooling system exceeds the predetermined maximum pressure, thereby venting the excess pressure. A spring on the over pressure release valve closes the valve again when the pressure is reduced below the allowable maximum.
A certain amount of atmospheric gases, for example, nitrogen and oxygen, are typically dissolved in the cooling fluid and these gases boil out of the coolant when it is heated. In addition, a certain amount of water and antifreeze evaporates as the coolant is heated, so that there is always a certain amount of gas in the cooling system. This gas accumulates at the top of the cooling system, which is typically where the radiator cap is located.
In addition, the liquid coolant expands as it is heated. The coolant expands enough to overflow and escape from the radiator through the over pressure release valve. The lost coolant is recovered in a coolant recovery tank, which is connected to the radiator by an air-tight hose.
As the engine cools, the volume of the coolant shrinks, eventually creating a partial vacuum in the cooling system. This partial vacuum opens a small valve in the bottom of the radiator cap, which we will call the "suction return valve," allowing the some of the coolant in the coolant recovery tank to be drawn into the radiator and cooling system. This cycle maintains a substantially full radiator and prevents loss of coolant. The prior art has devoted significant effort to developing radiator caps that control this cycle and prevent the cooling system from boiling over and allows the coolant to return to the radiator when the engine cools.
A preferred radiator cap for use in conjunction with the present invention is described and claimed in U.S. Pat. No. 4,185,751, issued to Moore et al. on Jan. 29, 1980 and entitled "Radiator Cap." This patent was assigned to Stant Manufacturing Company, Inc., in Connersville, Ind. at the time of issuance. This U.S. Pat. No. 4,185,751 is hereby incorporated by reference into this specification. Naturally, the present invention may be used in conjunction with any radiator cap having both an over pressure release valve and a suction return valve.
The present invention improves on such radiator caps by automatically opening the suction return valve, or coolant recovery valve, when the engine is turned off and keeping the suction return valve open whenever the engine is not running, thereby removing pressure from the system whenever the engine is turned off. Using the present invention, pressure within the cooling system will be entirely released within about 15-45 seconds after the engine is turned off, depending on specific operating parameters and then current conditions. Further, the present invention maintains the cooling system at atmospheric pressure, regardless of the temperature of the engine, at all times when the engine is turned off.
Other radiator caps of the related art have also been patented. Some of these caps are discussed below.
U.S. Pat. No. 4,196,822, issued to Avrea on Apr. 8, 1980 (Avrea '822), discloses a "Monolithic Radiator Cap for Sealed Pressurized Cooling System" comprising a radiator cap that remains sealed whenever it is seated in the radiator filler neck and that insures that any overflow of steam or hot liquid will be discharged through the overflow tube. An internal jacket around the main pressure spring is a distinctive feature of Avrea '822.
U.S. Pat. No. 4,185,751, issued to Moore et al. on Jan. 29, 1980 (Moore et al. -751) discloses a "Radiator Cap" comprising a first valve for admitting fluid into the radiator from the radiator overflow tank when the radiator is at atmospheric pressure. This valve remains open until fluid flow out of the radiator due to increased temperature and pressure during operation closes it. A second valve comprises an over pressure valve that releases fluid when the system becomes overheated.
U.S. Pat. No. 4,079,855, issued to Avrea on Mar. 21, 1978 (Avrea '855) discloses a "Monolithic Radiator Cap For Sealed Pressurized Cooling System" which is, for our purposes, virtually the same as the radiator cap disclosed in Avrea '822, discussed above. Avrea '855 and Avrea '822 originated from the same parent patent application, although each includes some material not found in the other.
U.S. Pat. No. 3,062,400, issued to Humbert on Nov. 6, 1962 (Humbert '400), discloses "Safety Valved Pressure Caps" comprising a manually operated pressure release valve that allows a person to relieve the pressure on an engine cooling system by actuating a lever on the exterior of the top surface of the cap. This cap includes an over pressure release valve and a smaller suction return valve, as do most modern radiator caps. The unique feature of this cap is the lever-handle on the exterior top surface of the cap, which provides a means for manually opening the pressure release valve, that is, the large valve that seats against the throat of the radiator. When the external lever is manually lifted, it tilts the pressure release valve upward, thereby allowing pressure to escape from the radiator. Using this cap, however, requires lifting the hood of the vehicle to reach the cap and then manually lifting the hot lever to release the pressure. Some hot liquid and gas can be expected to vent through the openings in the cap that are penetrated by the lever mechanism. This procedure is very awkward and unsafe for most people.
Each of the above references discloses a radiator cap having a valve for releasing excess cooling system pressure in a liquid cooled engine when the pressure of the fluid inside the radiator exceeds a predetermined level. Also disclosed in each of the references is a suction return valve for admitting fluid into the radiator from an overflow tank when the pressure inside the radiator drops as the engine and radiator cool. Also disclosed is a manually operated lever-actuated valve in a radiator cap for manually releasing the pressure in an engine cooling system.
Not shown in the references discussed above, however, is any mechanism for automatically releasing pressure from a cooling system as soon as the engine is turned off, that is, prior to any cooling. Nor do the references disclose any mechanism for maintaining the cooling system at atmospheric pressure from the time the engine is turned off until it is started again. In summary, the related art references do not disclose any automatic mechanism for quickly relieving unnecessary pressure from the cooling system, that is, as soon as the engine is turned off.
Therefore, there is a need for a device that automatically relieves all superatmospheric pressure from a vehicle cooling system when the engine is turned off and prevents any pressure from redeveloping as long as the engine is turned off. The present invention accomplishes this result and thereby significantly extends the life of cooling system components, such as hoses, and prevents accidental burns and scalds that could otherwise result from hot liquids being forced out of a radiator by the over pressure within the radiator.